digraph G {
  
  q0[shape = point];
  q1[label = "{}", shape = circle];
  q2[label = "{p}", shape = circle];
  q3[label = "{q}", shape = circle];
  q4[label = "{p, q}", shape = circle];
  {rank=same; q2, q3}
  q0 -> q1;
  q1 -> q2;
  q1 -> q3;
  q2 -> q4;
  q3 -> q4;
  q4 -> q2;
  }
